GARDAI fear that a new alliance between the Real IRA and three other terror factions presents a fresh threat.

The merger was formed during the summer after previous attempts to coalesce some of the dissident republican groups had failed.

And it has ensured that the threat level, currently listed as severe in Northern Ireland, will remain at its current status.

The Real IRA is reckoned by the garda anti-terrorist section to contain a hardcore of 50 paramilitary activists on this side of the Border, backed up by another layer of about 50 'facilitators' and support from some family members and associates.

Up until the merger, the group was divided into four principal factions, led by 'commanders' in Dublin, Co Louth, Derry and Belfast.

But the Dublin-based leader, a Corkman living in Tallaght, got into a dispute with Alan Ryan and lost the support of his group, which is largely based on the northside of the capital.

The Real IRA also has pockets of support in Louth-Monaghan, Meath, Kildare, Wexford-Waterford, Clare, Cork and, to a lesser extent, in Limerick, where most dissidents are linked to the Continuity IRA.

These two groups and the self-styled 'Oglaigh na hEireann', which split from the Real IRA, are mainly confined to logistical operations in the Republic, manufacturing homemade explosives, acquiring weaponry, stealing cars and providing back-up support for terror units in the North.

As a result of the merger, the PSNI reckons the new group has a membership of between 250 and 300 military activists, backed up by associates.

Also part of the alliance is a section of an east Tyrone republican group, which is believed to be responsible for the murder of Constable Ronan Kerr last year, and a gang of previously non-aligned dissidents from Belfast who badly injured PSNI constable and GAA player Peadar Heffron in 2010.

The fourth faction in the merger is the Republican Action Against Drugs, a Derry-based outfit comprised of former Provisional IRA activists.

Anti-terror officers said last night that the involvement of the other three groups with the Real IRA would provide them with a larger skills base and greater terrorism expertise.

But the alliance was also more likely to result in personal differences and had potential for an early split because of the number of 'egos' involved, officers pointed out.

Gardai said there was no obvious successor to take charge of the group formerly controlled by Ryan and that this could also lead to a rift, with three or four possible contenders.